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<html lang="en">
<head>
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    <meta http-equiv="X-UA-Compatible" content="IE=edge">
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    <title>Document</title>
    <style>
        *{
            margin:0;
            padding:0;
        }
        div{
            height:300px;
            width:200px;
            background-color: aqua;
            /* margin:auto; */
            /* position: fixed;
            left:50%;
            top:50%;
            margin-left:-50px;
            margin-top:-50px; */

            position: fixed;
            left:0;
            top:0;
            right:0;
            bottom:0;
            margin:auto;
        }
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</head>
<body>
    <div>
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</body>
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